Measurements of flow patterns around a wide wing-wall abutment in floodplain
Yeh, Yi Min
Date of Issue2018
School of Civil and Environmental Engineering
Scour around bridge support structures such as piers and abutments, is a widespread problem. As removal of ground materials results in lowering of stream bed, this will make the bridge more susceptible to structure failure. Bridge failure is a great concern which could cause significant transport disruption, economic loss, and in the worst case, the loss of lives. In order to better estimate the characteristics of scour formed for corrective actions, it is important to be able to predict the flow in scouring process around piers and abutments. The objective of this study is to examine the flow pattern around a wide 45° wing-wall (WW) abutment in a stabilized scour hole in a 19 m two-stage channel under clear water scour condition. In this experiment, Acoustic Doppler Velocimeter (ADV) were used for velocities measurements. Experiment was conducted in a laboratory ﬂume of 19 m long and 1.6 m wide, having a wing-wall abutment with transverse length of 20 cm situated in the sand bed located at the floodplain. Observations of 2 scour holes and 1 deposition ridge formed around the abutment were made. The sand bed was stabilized using chemical (adhesive spray) to reduce disturbance of geometry during flow measurements. This study is a continuation of the experiment done by Kenny (2018) whereby he measured and presented the flow patterns upstream of the scoured bed. Kenny’s experimental set-up was used in this study and the flow patterns downstream of the scoured bed were measured and discussed. Due to the location of downstream scour hole, flow measurements of some areas used wire bundles rather than wire frame to generate bubble. The results of the ﬂow ﬁeld in terms of the velocity vectors as well as contours of turbulent intensities, turbulent kinetic energy and the Reynold shear stress in the scour hole are presented. Vector plots of flow field showed the presence of vortex associated with the sudden expansion of channel and primary vortex extended from upstream. The flow is mostly downwards near the abutment. The bed shear stresses are estimated from Reynold shear stresses. At the sections where there is no scour hole, the 3 components turbulent intensity contours show a general decreasing trend close to the abutment. On the other hand, at the sections where there is scour hole, highest value out of the 3 components contours are observed to be on top of the scour hole.
Final Year Project (FYP)
Nanyang Technological University